Semiconductor Light-Emitting Diode and Method for Producing a Semiconductor Light-Emitting Diode

ABSTRACT

A semiconductor light-emitting diode ( 10 ) is proposed having at least one p-doped light-emitting diode layer ( 4 ), an n-doped light-emitting diode layer ( 2 ) and an optically active zone ( 3 ) between the p-doped light-emitting diode layer ( 4 ) and the n-doped light-emitting diode layer ( 2 ), having an oxide layer ( 8 ) consisting of a transparent conductive oxide, and having at least one mirror layer ( 9 ), wherein the oxide layer ( 8 ) is disposed between the light-emitting diode layers ( 2, 4 ) and the at least one mirror layer ( 9 ), and comprises a first boundary surface ( 8   a ) which faces the light-emitting diode layers ( 2, 4 ) and a second boundary surface ( 8   b ) which faces the at least one mirror layer ( 9 ), and wherein the second boundary surface ( 8   b ) of the oxide layer ( 8 ) has less roughness (R 2 ) than the first boundary surface ( 8   a ) of the oxide layer ( 8 ).

The invention relates to a semiconductor light-emitting diode and amethod for producing a semiconductor light-emitting diode.

This patent application claims priority of German patent application 102008 011 847.8 and German patent application 10 2008 027 045.8, whosedisclosure contents are hereby included by reference.

Semiconductor light-emitting diodes have a layer stack consisting ofsemiconductor layers whose materials are specifically selected (withrespect to base material and dopant) and are adapted to each other inorder to set to a predetermined extent the optoelectronic properties andthe electronic band structure within the individual layers and at thelayer boundaries. At the transition between two adjacent, mutuallycomplementarily doped light-emitting diode layers (p-doped and n-doped),an optically active zone is created which emits electromagneticradiation when current flows through the semiconductor layer stack. Thegenerated radiation is initially emitted in all directions, i.e., onlypartly in the emission direction of the semiconductor light-emittingdiode. In order to reflect the proportion of the radiation emitted tothe opposite side of the semiconductor layer stack back in the emissiondirection, an oxide layer, consisting of a transparent conductive oxide,and one or several mirror layers are provided behind the semiconductorlayer stack. One portion of the electromagnetic radiation impinging uponthe mirror layers is reflected depending upon the difference in theoptical refractive indices of the layers, upon the conductivity of themirror layer, upon the transparency of the oxide layer as well as uponthe thickness of the oxide layer and of the preceding layers towards theoptically active zone. In order to increase the reflected portion,conventionally in addition to the layer thicknesses primarily thematerial properties and material compositions of the respective layersare modified and optimised.

If the portion of electromagnetic radiation which impinges upon themirror layer and is reflected back by the mirror layer could beincreased, then the luminous efficiency of semiconductor light-emittingdiodes could be increased.

This is made possible by a semiconductor light-emitting diode accordingto any one of Claims 1 and 2 as well as by a method according to Claim14.

A semiconductor light-emitting diode is provided having at least onep-doped light-emitting diode layer, an n-doped light-emitting diodelayer and an optically active zone between the p-doped light-emittingdiode layer and the n-doped light-emitting diode layer, having an oxidelayer of a transparent conductive oxide, and having at least one mirrorlayer, wherein the oxide layer is disposed between the light-emittingdiode layers and the at least one mirror layer, and comprises a firstboundary surface which faces the light-emitting diode layers and asecond boundary surface which faces the at least one mirror layer, andwherein the second boundary surface of the oxide layer has lessroughness than the first boundary surface of the oxide layer.

Furthermore, a semiconductor light-emitting diode is provided in whichthe second boundary surface of the oxide layer has a roughness less than1.0 nm.

Forming the mirror layer on the second boundary surface of reducedroughness ensures that the degree of reflection at the boundary surfacebetween the oxide layer and the mirror layer is increased, whereinprimarily the portions of radiation impinging at large angles ofincidence are reflected to a greater extent.

If the oxide layer is provided with a layer thickness of more than 5 nm,then it is ensured that irregularities in the first boundary surface ofthe oxide layer, which irregularities are caused by the roughness of theunderlying uppermost semiconductor layer, are evened out and thus theroughness of the second boundary surface of the oxide layer is notadversely influenced thereby.

If the p-doped light-emitting diode layer is disposed closer to theoxide layer than the n-doped light-emitting diode layer, then the oxidelayer and the mirror layer are located on the p-side of thesemiconductor light-emitting diode. Although connecting the oxide layeron that side involves increasing the operating voltage of thesemiconductor light-emitting diode, this can be compensated for as willbe described hereinafter.

According to one development, a p-doped semiconductor layer is disposedbetween the p-doped light-emitting diode layer and the oxide layer whichp-doped semiconductor layer has a dopant concentration which is at leastas large as the dopant concentration of the p-doped light-emitting diodelayer. The p-doped semiconductor layer protects the p-dopedlight-emitting diode layer from crystal lattice damage when depositingthe oxide layer.

According to a first embodiment, the first boundary surface of the oxidelayer adjoins the p-doped semiconductor layer.

According to an alternative second embodiment, provision is made that ann-doped semiconductor layer is disposed between the p-dopedsemiconductor layer and the oxide layer, and that the oxide layeradjoins the n-doped semiconductor layer. As a result, a low-impedanceconnection of the oxide layer to the semiconductor layer stack isachieved.

According to one development, a non-doped semiconductor layer isprovided between the p-doped semiconductor layer and the n-dopedsemiconductor layer. Together with the two doped semiconductor layers,this non-doped semiconductor layer forms a tunnel contact, wherein thecontact resistance of the tunnel contact is more than compensated for bythe low-impedance connection of the oxide layer via the n-dopedsemiconductor layer and the required operating voltage is thus reducedon the whole.

The oxide layer is preferably electrically conductive.

Suitable materials for the oxide layer are, for example, zinc oxide,indium tin oxide or indium zinc oxide.

Provided the mirror layer directly adjoins the second boundary surfaceof the oxide layer, the second boundary surface of the oxide layersimultaneously forms a mirror surface with a particularly low roughness.

According to one embodiment, the mirror layer includes at least onemetallic mirror layer.

Suitable materials for the metallic mirror layer are, in particular,gold, silver or aluminium, wherein gold is suitable for reflection inthe infrared range, silver is suitable for reflection in the visiblewavelength range and aluminium is suitable for reflection in the UVrange.

According to one further embodiment—as an alternative to the metallicmirror layer or in addition thereto—at least one dielectric mirror layeris provided. In particular in combination with the metallic mirrorlayer, the dielectric mirror layer increases the reflection coefficientof the reflector on the rear side of the semiconductor light-emittingdiode.

Suitable materials for the dielectric mirror layer are, for example,glass, silicon oxide, silicon nitride or silicon oxynitride.

According to one development, provision is made that the dielectricmirror layer is disposed between the oxide layer and the metallic mirrorlayer and comprises local recesses in which the metallic mirror layerextends as far as to the second boundary surface of the oxide layer. Asa result, the metallic mirror layer forms contacts to the transparentconductive oxide layer, on the basis of which lateral current spreadingoccurs in the oxide layer over the entire surface area of thesemiconductor layer stack.

The base material suitable for the light-emitting diode layers can be,for example, binary, ternary or quaternary III-V semiconductormaterials, in particular those which contain at least one of theelements aluminium, gallium and indium and at least one of the elementsnitrogen, phosphorus and arsenic. Examples thereof are aluminiumnitride, aluminium indium nitride, gallium nitride, aluminium galliumnitride, indium gallium nitride and indium gallium arsenide phosphide.

The method for producing the semiconductor light-emitting diode includes

-   -   forming at least one p-doped light-emitting diode layer and an        n-doped light-emitting diode layer,    -   depositing a transparent conductive oxide, whereby an oxide        layer is formed which comprises a first boundary surface which        faces the light-emitting diode layers, wherein the oxide layer        is deposited by means of HF-assisted DC sputtering and in doing        so a second boundary surface of the oxide layer opposing the        first boundary surface is produced and has less roughness than        the first boundary surface of the oxide layer, and    -   forming at least one mirror layer above the second boundary        surface of the oxide layer.

By virtue of the fact that the oxide layer consisting of the transparentconductive oxide is deposited by means of HF-assisted DC sputtering, itssecond boundary surface has less roughness than its first boundarysurface, and in particular the roughness of the second boundary surfaceis less than 1.0 nm. In the finished semiconductor light-emitting diode,this results in a greater reflection or mirror effect at the boundarysurface between the oxide layer and the mirror layer.

If the oxide layer is deposited having a layer thickness of at least 5nm, then as a result irregularities in the first boundary surface of theoxide layer, which irregularities are caused by the roughness of theunderlying uppermost semiconductor layer, are evened out and theroughness of the second boundary surface of the oxide layer cannot beadversely influenced thereby.

According to one development, a p-doped semiconductor layer is depositedonto the p-doped light-emitting diode layer and has a dopantconcentration which is at least as large as the dopant concentration ofthe p-doped light-emitting diode layer. The p-doped semiconductor layerprotects the p-doped light-emitting diode layer from crystal latticedamage when sputtering-on the oxide layer.

If a non-doped semiconductor layer and an n-doped semiconductor layerare furthermore deposited over the p-doped semiconductor layer and theoxide layer is sputtered onto the n-doped semiconductor layer, then alow-impedance connection of the oxide layer is created via the n-dopedsemiconductor layer; the p-doped, non-doped and n-doped semiconductorlayers thereby form a tunnel contact whose contact resistance is morethan compensated for by the low-impedance connection of the oxide layerto the n-doped semiconductor layer.

According to one development, forming the mirror layer includesdepositing at least one dielectric mirror layer, etching recesses intothe dielectric mirror layer and depositing at least one metallic mirrorlayer onto the dielectric mirror layer; as a result the metallic mirrorlayer forms contacts to the oxide layer in the recesses of thedielectric mirror layer, on the basis of which contacts lateral currentspreading occurs in the oxide layer over the entire surface area of thesemiconductor layer stack.

Several exemplary embodiments of the invention will be describedhereinafter with reference to the Figures, in which:

FIG. 1 shows a first exemplary embodiment of a semiconductorlight-emitting diode,

FIG. 2 shows a second exemplary embodiment of a semiconductorlight-emitting diode,

FIG. 3 shows a third exemplary embodiment of a semiconductorlight-emitting diode having several mirror layers,

FIG. 4 shows a fourth exemplary embodiment of a semiconductorlight-emitting diode having several mirror layers, and

FIG. 5 shows an enlarged schematic detail view of a provisionalsemiconductor product during the production of a semiconductorlight-emitting diode according to any one of FIGS. 1 to 4.

FIG. 1 shows a cross-sectional view of a first exemplary embodiment of asemiconductor light-emitting diode 10 which comprises a semiconductorlayer stack 20. Although the generated electromagnetic radiation, whichis in the visible range, infrared range or UV range, is firstly emittedin all directions, it is to be emitted as completely as possible througha radiation exit surface 25 of a radiation exit layer 1 (at the bottomin FIG. 1) which is disposed on the side of the semiconductor layerstack remote from the oxide layer and the mirror layer. The radiationexit layer 1 is either a substrate layer, which remains after all layershave been grown onto the substrate and the substrate has been virtuallycompletely etched back (thin film LED), or a semiconductor layer whichhas been grown onto the substrate prior to the actual light-emittingdiode layers, the substrate having been completely removed at a latertime.

The further layers are grown onto the radiation exit layer 1 as follows:Firstly, an n-doped light-emitting diode layer 2 and a p-dopedlight-emitting diode layer 4 are deposited. The mutually oppositelydoped light-emitting diode layers 2, 4, form a light-emitting diodelayer sequence, as can be seen in FIG. 1 by the dashed lines. Anoptically active zone 3 is created at the boundary surface between thetwo semiconductor layers 2, 4 and serves to emit electromagneticradiation when a sufficient bias voltage of appropriate polarity isapplied to the light-emitting diode layers 2, 4. The n-dopedlight-emitting diode layer 2 is in this case doped with silicon and thep-doped light-emitting diode layer 4 is doped with magnesium, whereinthe base material of the light-emitting diode layers 2, 4 is a III/Vsemiconductor material in each case. The radiation exit layer 1 is usedto protect and electrically insulate the lower n-doped light-emittingdiode layer 2.

On the side of the light-emitting diode layer sequence on which thep-doped light-emitting diode layer 4 is disposed (i.e., at the top inFIG. 1), an oxide layer 8 consisting of a transparent conductive oxideis deposited. In particular, the oxide layer 8 contains a transparentelectrically conductive oxide.

The oxide layer is used for current spreading in the lateral directionin parallel with the layer boundaries as well as for obviating undesiredmigration between the mirror layer and the semiconductor layer stack.FIG. 1 shows an exemplary embodiment in which the oxide layer 8 is notdeposited directly onto the p-doped light-emitting diode layer 4 butrather firstly a p-doped semiconductor layer 5 is deposited (in order toprotect the p-doped light-emitting diode layer 4), said p-dopedsemiconductor layer having a dopant concentration which is at least aslarge as that of the p-doped light-emitting diode layer 4.

The oxide layer 8 consisting of a transparent conductive oxide (TCO) isthen deposited onto the p-doped semiconductor layer 5. In doing so theroughness of the top side of the p-doped semiconductor layer 5 providesthe roughness R1 of the first boundary surface 8 a of the oxide layer 8.The first boundary surface of the oxide layer is the boundary surfacewhich faces the semiconductor layer stack (and in particular directlyadjoins the uppermost, lastly deposited semiconductor layer of the layerstack).

Indium tin oxide, indium zinc oxide or zinc oxide for example aresuitable as the transparent conductive oxide. In the case of zinc oxide,the conductivity can be increased by doping with aluminium or gallium.Furthermore, instead of a single oxide layer a layer sequence of severaloxide layers can also be provided.

The oxide layer is deposited by means of HF-assisted DC sputtering; as aresult it acquires an upper second boundary surface 8 b which has aparticularly low roughness R2. After the oxide layer 8 has beensputtered-on, its second boundary surface 8 b is initially exposed;finally the mirror layer 9 (in particular a metallic mirror layer 19) isdeposited thereon according to FIG. 1.

The boundary surfaces between the respective layers of the semiconductorlayer stack and between the semiconductor layer stack, the oxide layerand the mirror layer always have a particular roughness. The roughnessis mostly provided as a numerical value (for example in nm) with theaddition “rms” (root mean squared—deviation from the ideal boundarysurface plane, i.e., standard deviation of the variation in height ofthe boundary surface or surface). The average is determined over asurface region of the respective surface or boundary surface. Theroughness of boundary surfaces within the layer sequence for thesemiconductor light-emitting diode 10 is conventionally at best between1.5 and 5 nm, however it can also be considerably higher and more than20 nm. Deviations from the ideal crystal lattice, e.g., locally varyinggrowth conditions or lattice distortions, even as a result of dopants,contribute in particular to the roughness.

When producing a semiconductor light-emitting diode, conventionally thematerials and material combinations of the respective layers (includingdopants) are optimised and adapted to each other. Furthermore, layerthicknesses and refractive indices of the layers are optimised in orderto achieve constructive interference of the electromagnetic radiationreflected at the boundary surfaces and thus a high luminosity for thelight-emitting diode. The influence of variations in height of the layerboundaries, which are caused by roughness and are smaller than thewavelength of the radiation to be reflected by two to three orders ofmagnitude (corresponding to a factor of 100 to 1000), is, however,mostly neglected.

The second boundary surface of the oxide layer, which is remote from thesemiconductor layer stack, i.e., which faces the mirror layer,conventionally has even more roughness than the first boundary surfaceof the oxide layer since the transparent conductive oxide generally doesnot grow in a monocrystalline manner but rather grows in apolycrystalline or amorphous manner.

However, depositing the oxide layer 8 by means of an HF-assisted DCsputtering process, as proposed herein, produces particularly lowroughness R2 on the second boundary surface 8 b of the oxide layer andthus increases the reflectivity of the mirror layer to be depositedthereon. The HF-assisted DC sputtering process will now be discussedwith reference to FIG. 5.

The mirror layer 9 is deposited onto the second boundary surface 8 b(exposed after performing the sputtering process) of the oxide layer 8.The mirror layer 9 is deposited by means of PVD (Physical VapourDeposition) or CVD (Chemical Vapour Deposition), in particular by meansof PECVD (Plasma Enhanced Chemical Vapour Deposition), MBE (MolecularBeam Epitaxy), IBE (Ion Beam Etching) or by thermal evaporation. In thisexemplary embodiment, the mirror layer 9 is a metallic mirror layer 19which consists of gold, silver or aluminium or an alloy which containsat least one of these metals. The metallic mirror layer 19 can alsoinclude several layers each being made of a metal or a metal alloy.

The materials and layer thicknesses of the oxide layer 8 and the mirrorlayer 9 are adjusted to each other such that the portion ofelectromagnetic radiation emitted by the optically active zone 3 whichis emitted in the direction of the oxide layer and the mirror layer isreflected as completely as possible at the second boundary surface 8 bof the oxide layer 8. The angle of incidence of the radiation to bereflected is subject to a statistical distribution and can basically beany value between 0 degrees and 90 degrees relative to the surfacenormal of the reflecting boundary surface of the mirror layer. The lowroughness of the second boundary surface 8 b of the oxide layer 8results in that even in the case of large angles of incidence relativeto the surface normal of the second boundary surface 8 b, overall alarger proportion of the impinging electromagnetic radiation isreflected. As a result, the intensity of the electromagnetic radiationemitted by the semiconductor light-emitting diode is increased.

FIG. 2 shows a second exemplary embodiment of a semiconductorlight-emitting diode in which in addition to the layers illustrated inFIG. 1 a non-doped semiconductor layer 6 and an n-doped semiconductorlayer 7 are also provided and are disposed between the p-dopedsemiconductor layer 5 and the oxide layer 8. The n-doped semiconductorlayer 7 facilitates the connection of the oxide layer 8 consisting ofthe transparent conductive oxide to the semiconductor layer stack 20.The non-doped semiconductor layer 6 is disposed between the p-dopedsemiconductor layer 5 and the n-doped semiconductor layer 7. Thesequence of the semiconductor layers 5, 6 and 7 forms a tunnel contactto the actual light-emitting diode layer sequence consisting of thelight-emitting diode layers 4 and 2. A slight increase in the operatingvoltage through the tunnel contact is more than compensated for by thelow-impedance connection of the oxide layer 8 via the n-dopedsemiconductor layer 7.

The same base materials used for the light-emitting diode layers 2, 4are suitable for the layers 5, 6 and 7. In this exemplary embodiment,the layer thickness of the doped semiconductor layers 5, 7 is smallerthan 30 nm; for example it is between 3 and 20 nm. Furthermore, in thisexemplary embodiment, the layer thickness of the non-doped semiconductorlayer 6 is smaller than 20 nm; for example it is between 1 and 10 nm.The remainder of the embodiment described for FIG. 1 is applicable forFIG. 2.

The layers, illustrated in FIGS. 1 and 2, of the semiconductor layerstack 20 are deposited for example by means of CVD (Chemical VapourDeposition) before the oxide layer 8 is deposited onto the semiconductorlayer stack 20 and the mirror layer 9 is deposited thereon. On the lowerside of the semiconductor layer stack 20 the substrate is subsequentlythinned or completely removed so that the radiation exit layer 1 isexposed.

Whilst FIGS. 1 and 2 show exemplary embodiments in which the oxide layer8 directly adjoins the lower side of a metallic mirror layer 19, FIGS. 3and 4 show exemplary embodiments having an additional dielectric mirrorlayer 18 between the oxide layer 8 and the metallic mirror layer 19. InFIG. 3, the semiconductor layer stack 20 has the same construction as inFIG. 1; in FIG. 4 it has the same construction as in FIG. 2. Theexplanations with respect to FIGS. 1 and 2 are thus also applicable forFIGS. 3 and 4 respectively.

According to FIGS. 3 and 4, the oxide layer 8 is deposited onto theuppermost semiconductor layer 5 and 7 respectively by means ofHF-assisted DC sputtering. A dielectric mirror layer 18 (e.g.,consisting of silicon oxide) is initially deposited onto the secondboundary surface 8 b of said oxide layer. Recesses 11 are then etchedinto the dielectric mirror layer 18 and a metallic mirror layer 19 isdeposited onto the dielectric mirror layer 18. The material of themetallic mirror layer 19 extends in the recesses of the dielectricmirror layer 18 as far as to the second boundary surface 8 b of theoxide layer 8 and thus forms at this location linked contacts to theoxide layer 8. On the basis of the linked contacts, lateral currentspreading then occurs in the transparent conductive oxide layer 8 overthe entire surface area of the semiconductor layer stack 20.

In this exemplary embodiment, the mirror layer 9 includes a dielectricmirror layer 18 and also a metallic mirror layer 19. Since the mirrorlayers 9; 18, 19 are deposited after the oxide layer 8, the lowroughness R2 of the second boundary surface 8 b of the oxide layer 8also causes the roughness of the boundary surface between the mirrorlayers 18 and 19 to be reduced. As a result, the reflection coefficientof the mirror layer stack is further increased since the low roughnessof the second boundary surface of the oxide layer also causes theroughness of the boundary surfaces of subsequent mirror layers to bereduced to a certain extent. The remainder of the embodiment describedfor FIGS. 1 and 2 is applicable for FIGS. 3 and 4.

In the case of the above-mentioned exemplary embodiments, the followingdopant concentrations are provided: The n-doped light-emitting diodelayer 2 has a dopant concentration of less than 1×10²⁰/cm³, inparticular less than 1×10¹⁹/cm³. The p-doped light-emitting diode layer4 has a dopant concentration of less than 2×10²⁰/cm³. The dopantconcentration of the p-doped semiconductor layer 5 is at least as highas that of the p-doped light-emitting diode layer 4 and is more than2×10²⁰/cm³. The dopant concentration of the n-doped semiconductor layer7 is higher than that of the n-doped light-emitting diode layer 2 and ismore than 2×10²⁰/cm³. Therefore, each of the two semiconductor layers 5,7 is doped to a greater extent than the respective light-emitting diodelayers 4, 2 of the same dopant type. The p-doped layers are doped withmagnesium and the n-doped layers are doped with silicon.

Alternatively, the dopant concentration of the n-doped semiconductorlayer 7 can also be less than the dopant concentration of the n-dopedlight-emitting diode layer 2.

FIG. 5 shows an enlarged schematic detail view of a provisionalsemiconductor product for producing the semiconductor light-emittingdiode according to any one of FIGS. 1 to 4, in fact after sputtering-onthe oxide layer 8. An upper partial region of the uppermost layer of thesemiconductor layer stack 20 as well as the oxide layer which issputtered thereon and is made of the transparent conductive oxide areillustrated. The uppermost semiconductor layer is either the p-dopedsemiconductor layer 5 from FIG. 1 or 3 or the n-doped semiconductorlayer 7 from FIG. 2 or 4.

If the oxide layer 8 is deposited onto the top side of the uppermostsemiconductor layer 5 or 7, then the roughness of the uppermostsemiconductor layer provides the roughness R1 of the lower firstboundary surface 8 a of the oxide layer 8; it is typically more than 1.5nm rms but it can also be substantially higher—depending upon the methodof deposition for the uppermost semiconductor layer, its base materialand its dopant concentration. In the case of a p-doped semiconductorlayer 5 (FIG. 1 or 3) consisting of gallium nitride, the roughness ofits top side is between 1.2 to 1.8 nm.

The HF-assisted DC sputtering method for depositing the oxide layer 8consisting of the transparent conductive oxide ensures that theroughness R2 of its second boundary surface 8 b, as illustrated in FIG.5, is less than the roughness R1 of the first boundary surface 8 a, inparticular less than 1.0 nm or even 0.5 nm.

In the exemplary embodiments described here, the oxide layer 8 issputtered-on with a layer thickness of between 1 and 50 nm, wherein alarger layer thickness can also be selected. If the oxide layer isdeposited with a minimum layer thickness of e.g., 5 nm, thenirregularities, which arise from the underlying semiconductor layer 5 or7, are evened out during the sputtering-on of the oxide layer. It isthereby ensured that the roughness R2 of the second boundary surface 8 bof the oxide layer 8 is influenced only by the HF-assisted DC sputteringmethod but not by variations in height of the deeper-lying semiconductorlayers.

The mirror layers which are disposed on the oxide layer (deposited bymeans of the HF-assisted DC sputtering) have extremely smooth reflectivesurfaces. In addition, the uppermost semiconductor layer of thesemiconductor layer stack, which layer is exposed prior to sputtering-onthe oxide layer 8, is barely damaged by the HF-assisted DC sputteringmethod.

The HF-assisted DC sputtering method, which is known per se, is in thiscase used to deposit the oxide layer 8 of the transparent conductiveoxide onto the uppermost layer of the semiconductor layer stack 20 forthe light-emitting diode. During the HF-assisted DC sputtering method, ahigh-frequency alternating voltage is superimposed onto an electricdirect voltage. The electric power supplied for sputtering thus includesa direct current (DC) portion and a high-frequency (HF) portion. Thefrequency of the high-frequency power portion is for example 13.56 MHz.During sputtering, the combined DC/HF power is supplied for example toan electrode disposed in a sputtering chamber.

The second boundary surface 8 b of the oxide layer 8 deposited by meansof the HF-assisted DC sputtering method, and the boundary surfaces ofthe further mirror layers 18, 19 deposited onto the second boundarysurface 8 b reflect a higher portion of the electromagnetic radiationimpinging thereon owing to the reduced roughness. This is particularlyapplicable for the radiation portions which impinge upon these boundarysurfaces at larger angles of incidence relative to the surface normal.

Owing to the increased reflection coefficient, the semiconductorlight-emitting diode 10 emits overall a greater intensity ofelectromagnetic radiation at its radiation exit surface 25.

The description made with reference to the exemplary embodiments doesnot restrict the invention. Rather, the invention encompasses any novelfeature and any combination of features, including in particular anycombination of features in the claims, even if this feature or thiscombination is not itself explicitly indicated in the claims orexemplary embodiments.

1. A semiconductor light-emitting diode (10) comprising: at least onep-doped light-emitting diode layer, an n-doped light-emitting diodelayer and an optically active zone between the p-doped light-emittingdiode layer and the n-doped light-emitting diode layer; an oxide layerof a transparent conductive oxide; and at least one mirror layer;wherein the oxide layer is disposed between the light-emitting diodelayers and the at least one mirror layer, and comprises a first boundarysurface which faces the light-emitting diode layers and a secondboundary surface (8 b) which faces the at least one mirror layer, andwherein the second boundary surface of the oxide layer has lessroughness than the first boundary surface of the oxide layer.
 2. Asemiconductor light-emitting diode comprising: at least one p-dopedlight-emitting diode layer, an n-doped light-emitting diode layer and anoptically active zone between the p-doped light-emitting diode layer andthe n-doped light-emitting diode layer; an oxide layer of a transparentconductive oxide; and at least one mirror layer; wherein the oxide layeris disposed between the light-emitting diode layers and the at least onemirror layer, and comprises a first boundary surface (8 a) which facesthe light-emitting diode layers and a second boundary surface whichfaces the at least one mirror layer, and wherein the second boundarysurface of the oxide layer has a roughness which is less than 1.0 nm. 3.The semiconductor light-emitting diode according to claim 1 or 2,wherein the oxide layer has a layer thickness greater than 5 nm.
 4. Thesemiconductor light-emitting diode according to claim 1 or 2, whereinthe p-doped light-emitting diode layer is disposed closer to the oxidelayer than the n-doped light-emitting diode layer.
 5. The semiconductorlight-emitting diode according to claim 1 or 2, wherein disposed betweenthe p-doped light-emitting diode layer and the oxide layer is a p-dopedsemiconductor layer which has a dopant concentration which is at leastas large as the dopant concentration of the p-doped light-emitting diodelayer.
 6. The semiconductor light-emitting diode according to claim 5,wherein the oxide layer adjoins the p-doped semiconductor layer with itsfirst boundary surface.
 7. The semiconductor light-emitting diodeaccording to claim 5, wherein an n-doped semiconductor layer is disposedbetween the p-doped semiconductor layer and the oxide layer, and in thatthe first boundary surface of the oxide layer adjoins the n-dopedsemiconductor layer.
 8. The semiconductor light-emitting diode accordingto claim 7, wherein a non-doped semiconductor layer is disposed betweenthe p-doped semiconductor layer and the n-doped semiconductor layer. 9.The semiconductor light-emitting diode according to claim 1 or 2,wherein the transparent conductive oxide of the oxide layer contains atleast one of the materials zinc oxide, indium tin oxide and indium zincoxide.
 10. The semiconductor light-emitting diode according to claim 1or 2, wherein the mirror layer adjoins the second boundary surface ofthe oxide layer.
 11. The semiconductor light-emitting diode according toclaim 1 or 2, wherein the mirror layer comprises at least one metallicmirror layer.
 12. The semiconductor light-emitting diode according toclaim 1 or 2, wherein the mirror layer includes at least one dielectricmirror layer.
 13. The semiconductor light-emitting diode according toclaim 12, wherein the dielectric mirror layer is disposed between theoxide layer and the metallic mirror layer and comprises local recessesin which the metallic mirror layer extends as far as to the secondboundary surface of the oxide layer.
 14. A method for producing asemiconductor light-emitting diode, wherein the method comprises thesteps of: forming at least one p-doped light-emitting diode layer and ann-doped light-emitting diode layer; depositing a transparent conductiveoxide, wherein an oxide layer is formed which comprises a first boundarysurface which faces the light-emitting diode layers, wherein the oxidelayer is deposited by means of HF-assisted DC sputtering and in doing soa second boundary surface of the oxide layer opposing the first boundarysurface is produced which has less roughness than the first boundarysurface of the oxide layer; and forming at least one mirror layer abovethe second boundary surface of the oxide layer.
 15. The method accordingto claim 14, wherein forming the at least one mirror layer includesdepositing at least one dielectric mirror layer, etching recesses intothe dielectric mirror layer and depositing at least one metallic mirrorlayer onto the dielectric mirror layer.